In a turbine, a plurality of disks are disposed in the axial direction of a rotary shaft. In the peripheries of these disks, a large number of turbine rotor blades are implanted adjacent to each other in the circumferential direction. Between the turbine rotor blades adjacent to each other in the axial direction, stator blades are disposed which are provided in a casing covering the outside of the turbine rotor blades. Passing high-temperature combustion gas between the turbine rotor and stator blades rotationally drives the turbine rotor blades and the rotary shaft to drive, for example, a compressor and a generator.
On the side of the casing outside the rotor blades, a component is disposed which determines the clearance to the tips of the rotor blades. This component is often formed of a wear-prone honeycomb or coated with a special scratch-prone coating so that even if the component comes into contact with rotor blades due to causes such as an error in clearance control, damage to the rotor blades may be minimized.
If the clearance is large, gas leaks out through the clearance to decrease the efficiency of the turbine. Accordingly, ideally, the smaller clearance is the better. On the other hand, reducing the clearance increases the risk of the above-described contact with the component. However, in recent years, there has been a growing demand for clearances made as small as possible in relation to an increasing need for efficiency improvement. Accordingly, the risk of the above-described contact is inevitably increasing.
Examples of the above-described turbine rotor blade include, for example, a turbine rotor blade 50 having a fin 52 provided at a tip 51a of a blade portion 51 as shown in FIG. 6 (upper end portion of the blade portion 51 in FIG. 6). By providing the fin 52 at the tip 51a of the blade portion 51 as described above, the clearance between the turbine rotor blade 50 and the aforementioned component on the casing side is adjusted to be as small as possible.
Since turbine rotor blades are subjected to a high temperature environment as described previously, there are cases where a fin is damaged by aged deterioration such as oxidation or by contact with the casing-side component due to thermal expansion during operation. In such a case, as shown in FIG. 7, the fin is repaired by overlaying base material 53 with weld material 42 supplied in the form of a wire by welding using a welding heat source 41 (e.g., see Patent Literature 1). At this time, the base material 53 is overlaid with weld metal 54 by welding. The base material 53 is melted in a region above a fusion boundary 56 by the heat from the welding heat source 41, and becomes a heat-affected zone 55 affected by the heat in a region under the fusion boundary 56.    Patent Literature 1: JP-A-Hei-10-80767